Lithium bis(fluorosulfonyl) imide (FSO2)2N−Li+ (LiFSI), a method for the preparation thereof and use thereof in electrochemical devices are known, for instance by WO95/26056. Bis(fluorosulfonyl) imides of various onium cations are also known, for instance by WO99/40025.
Bis(fluorosulfonyl) imides have interesting properties in terms of ionic conductivity, useful for use as salt in the electrolyte of a battery, especially a lithium battery.
Bis(fluorosulfonyl)imide is prepared from bis(chlorosulfonyl)imide (HClSI), by chlorine/fluorine exchange with KF or HF. This method has many disadvantages. On the one hand, (chlorosulfonyl)imide is a product that decomposes violently in water. On the other hand, its synthesis is relatively complex. When KF is used for Cl/F exchange, the exchange strongly depends on the solvent in which the reaction takes place. Thus, tests implemented in nitromethane made by a specialist in industrial fluorine chemistry, have been abandoned, because the nitromethane causes the formation of dangerous nitrous vapors in the reactor. Attempts to find an alternative solvent have proved unsuccessful. The yield of the reaction and especially the formation of impurities such as FSO salt, probably resulting from the decomposition of (chlorosulfonyl)imide, make this kind of synthesis uninteresting at an industrial scale. When the Cl/F exchange is carried out with HF, it is necessary to operate at high temperatures (100° C. and above), and the yield of the reaction is at most about 60%, the product containing a significant amount of fluorosulfonic acid, probably resulting from the decomposition of bis(chlorosulfonyl)imide. This alternative process is also uninteresting at an industrial scale. Bis(fluorosulfonyl)imide synthesis has been abandoned by two important industrial specialists in fluorine chemistry, because furthermore, the raw product, HClSI, is difficult to access at an industrial scale.
Bis(fluorosulfonyl)imide can also be prepared by reacting fluorosulfonic acid with urea. This synthesis gives a non reproducible reaction yield (typically between 20 and 40%), it is very exothermic and the reaction medium is very corrosive. The process to separate bis(fluorosulfonyl)imide formed from the fluorosulfonic acid reagent is complex and makes the synthesis inconvenient on an industrial scale. Attempts to improve the process by carrying out the synthesis in a solvent were unsuccessful. The implementation of this synthesis method has also been abandoned by industrial specialists in fluorine chemistry.
It thus appears that the use of bis(fluorosulfonyl)imides is particularly complex to implement. Despite intensive efforts for nearly ten years in collaboration with renowned academic and industrial experts of fluorine chemistry, production on an industrial scale of bis(fluorosulfonyl)imides could not be implemented.
EP-0 850 920 describes ionic compounds in which the anion is a pentacycle, in particular of the triazole type, and the cation is a metallic cation, an organometallic cation or an onium ion.
Some of these compounds comprise a nitrile substituent on the pentacycle, for example:

These compounds have a low thermal stability because of the possible polymerization of the —CN. It is known that nitrile derivatives can form triazine bonds by addition reaction under the effect of heat. This makes it difficult to efficiently dry the hygroscopic lithium salts and highly coloured products are rapidly obtained when drying is carried out at a temperature of about 100° C. and more. Moreover, because of the presence of the —CN group, performances of these salts, during the cycling of a battery in which they are used, are insufficient relatively to a lithium electrode in polymer technology, and even worse with a liquid or gel electrolyte. The performances are also bad in lithium-ion batteries which have a carbon anode. The limited thermal stability can also be disadvantageous when the compounds are intended for use as ionic liquid.
The compounds (A), (B) and (C) are obtained from the corresponding diazonium. However, the diazonium compounds are potentially dangerous. Particularly, the one derived from 3-trifluoromethyl-5-amino-1,2,4-triazole is a powerful explosive in dry state, despite the presence of the —CF3 group.

Compounds I, II and III are obtained by reaction of sodium azide with the corresponding alkynes in an organic solvent. On the one hand, the alkynes used are uncommon and difficult to access compounds, and on the other hand, sodium azide is a dangerous compound, potentially explosive and very toxic. Hence, it is particularly difficult to develop such chemical processes at an industrial scale.
Other compounds described in EP-0 850 920 comprise a —SO2RF in which RF is a perfluoroalkyl group, for example compounds

These compounds are obtained from a perfluoroalkylsulfonic reactant and either a triazole diazonium or an alkyne. On the one hand, perfluoroalkylsulfonic reactants are obtained by electrofluorination and are expensive. On the other hand, the triazole diazonium and the alkynes have the drawbacks mentioned earlier. Moreover, the synthesis of the particular compound 3-trifluoromethyl-5-trifluoromethanesulfonyl-1,2,4-triazole is carried out in an flammable organic solvent and not in water as previously, which again increases the risk on an industrial scale. Considering the synthesis and precursors, a major specialist in fluorine chemistry has abandoned exploration of the synthesis of this product.
EP-0 850 920 further describes compounds which have two perfluoroalkyl substituents, for instance the compounds

4,5-ditrifluorométhyl-1,2,3-triazole is obtained by reaction of hexafluorobutyne with NaN3, which is a dangerous, potentially explosive and very toxic compound.
3,5-ditrifluoromethyl-1,2,4-triazole is obtained from trifluoroacetic acid and hydrazine by a process described in particular by Abdul-Ghani & Tipping, [J. Fluorine Chem., 72 (1995) 95], according to the following reaction scheme:

These products provide disappointing results especially in terms of electrochemical stability and of conductivity, CF3 groups alone being not enough electro attractive.